As disclosed in, for example, JP-A-2007-71596 corresponding to US 2007/0051599A1, a collision detector for detecting a collision to the side of a vehicle is known. In the conventional collision detector, a pressure sensor is installed inside a side door of the vehicle, and the collision is detected based on a change in pressure in the side door caused by deformation of the side door in the event of the collision. When the collision is detected, a side airbag or the like is activated so that an occupant can be protected from impact of the collision.
In the event of a collision to a side door of a vehicle, it is likely that a pressure increase in the side door due to deformation of the side door occurs at the same time as vibration of the side door due to not only the collision impact but also a movement of the vehicle. Accordingly, the pressure increase and the vibration are superimposed on each other and applied to a pressure sensor inside the side door. As a result, a detection value of the pressure sensor is derived from not only the pressure increase but also the vibration. For this reason, it is difficult to accurately detect the pressure change only inside the side door.
To avoid this disadvantage, the conventional collision detector disclosed in JP-A-2007-71596 uses a vibration sensor in addition to the pressure sensor. A diaphragm of the pressure sensor is exposed to sealed space inside the side door, but a diaphragm of the vibration sensor is isolated from the sealed space. A detection value of the vibration sensor is subtracted from a detection value of the pressure sensor so that an influence of the vibration of the side door on the detection value of the pressure sensor can be removed. In the conventional collision detector disclosed in JP-A-2007-71596, although the diaphragm of the pressure sensor is covered with a protector made of synthetic resin, the diaphragm of the vibration sensor is not covered with such a protector. Therefore, an influence of vibration of the protector on the detection value of the pressure sensor cannot be removed. In particular, in recent years, a protector for protecting inner electronic devices of a pressure sensor has become essential, and the demand for highly accurate collision detection performance has been increased. For these reasons, an influence of vibration of a protector on a detection value of a pressure sensor becomes concern.